Fig. 129 represents a section of step and riser, joined after the most approved method. In this, a represents the end of a block about 2 inches long, two or three of which, in the length of the step, are glued in the corner. The cove at b is planed up square, glued in, and stuck or moulded after the glue is set.
256. - Platform Stairs: the Cylinder. - A platform stairs ascends from one story to another in two or more flights, having platforms or landings between for resting and to change their direction. This kind of stairs, being simple, is easily constructed, and at the same time is to be preferred to those with winders, for the convenience it affords in use (Art. 250). The cylinder may be of any diameter desirable, from a few-inches to 3 or more feet, but it is generally small, about 6 inches. It may be worked out of one solid piece, but a better way is to glue together 3 pieces, as in Fig. 130; in which the pieces a, b, and c compose the cylinder, and d and e represent parts of the strings. The strings, after being glued to the cylinder, are secured with screws. The joining at 0 and 0 is the most proper for that kind of joint.
257.__Form of Lower Edge of Cylinder. - Find the stretch-out, de (Fig. 131), of the face of the cylinder, a b c, according to Art. 524; from d and e draw df and eg at right angles to de; draw kg parallel to de, and make hf and gi each equal to one riser; from i and f draw ij and fk parallel to hg; place the tread of the pitch-board at these last lines, and draw by the lower edge the lines k h and it; parallel to these draw m n and op, at the requisite distance for the dimensions of the string; from s, the centre of the plan, draw sq parallel to df; divide h q and qg each into two equal parts, as at v and w; from v and w draw v n and w o parallel to fd; join n and o, cutting qs in r; then the angles unr and rot, being eased off according to Art. 521, will give the proper curve for the bottom edge of the cylinder. A centre may be found upon which to describe these curves, thus: from u draw ux at right angles to m n; from r draw rx at right angles to no; then x will be the centre for the curve u r. The centre for the curve rt may be found in a similar manner. Centres from which to strike these curves are usually quite unnecessary; an experienced workman will readily form the curves guided alone by his practised eye.